1. Field of the Invention
This invention relates to deodorant sticks, and more particularly, to soap-based deodorant sticks.
2. Description of the Prior Art
Soap-based stick compositions for applying active ingredients to the skin are well known in the prior art. For instance, U.S. Pat. No. 2,900,306, discloses a deodorant cosmetic stick prepared by gelling a major amount of an alcohol of two to three carbon atoms by the addition of a minor amount of sodium stearate. A deodorant is added to this base, followed by the addition of from about 0.5% to 5% by weight of a water-soluble soap of myristic acid to improve the yielding properties of the stick. Similar sticks are described in U.S. Pat. Nos. 2,857,315 and 2,933,433, which disclose antiperspirant sticks having a base prepared by adding sodium stearate to either propylene glycol or alcohol. Using a glycol or alcohol in such a stick increases the cost considerably. Accordingly, if a less expensive alternative solvent could be found, it would be preferred.
One potential alternative solvent is water. Using water to form a stick is known in the prior art. For instance, U.S. Pat. No. 3,576,776, describes adhesive applicator crayons where the gelling component is a salt formed by combining an aliphatic carboxylic acid having from 8 to 36 carbon atoms with a cation selected from alkali metals, ammonium and lower alkyl ammonium. This salt is added to water, either alone or in combination with a water-miscible organic solvent, producing a gel to which an adhesive component is added. The preferred cation-carboxylic acid combination is sodium stearate.
A stick produced by gelling water with either sodium stearate or sodium palmitate lacks the necessary cosmetic attributes for applying active ingredients to human skin. Sodium palmitate produces a stick with excessive softness and poor heat ageing. Similarly, a stick produced from sodium stearate leaves a film on the skin which is flaky and lacks uniformity and smoothness. Furthermore, adding germicides and fragrances introduces additional problems such as stickiness and softness.
To a large extent, the problems described above are solved when a deodorant stick containing a germicide is produced by gelling water with a mixture of sodium stearate and sodium palmitate in a particular weight-ratio range. However, such a composition expands upon cooling, making the resulting stick difficult to extrude from its packaging. In addition, at temperatures in excess of 35.degree. C., such a stick begins to melt.
Accordingly, a need exists for means for reducing the tendency of such a stick to bind in its packaging and increasing such a stick's high temperature stability.